1. Field of Invention
This invention relates to synthetic resins, particularly high molecular weight, normally solid polymers of alkylene oxides and carbon dioxide. Such polymers are referred to in the art as poly(alkylene carbonates), and frequently in this specification as "PACs" or in the singular as "PAC".
2. Description of Prior Art
PACs have been known for many years, but have not achieved widespread commercial use for a number of reasons. One reason is that up to now those polymers made from the more readily commercially available alkylene oxides such as ethylene oxide and propylene oxide are amorphous. They have no definite melting points, and, compared to synthetic resins in general, have low glass transition temperatures and low decomposition temperatures. For example, the typical T.sub.g of poly(ethylene carbonate), ("PEC"), of 50,000 number-average molecular weight is 10.degree.-28.degree. C., and the typical T.sub.g of poly(propylene carbonate), ("PPC"), of 50,000 number-average molecular weight is 40.degree. C. The typical decomposition temperature of PEC is 220.degree. C., and of PPC is 250.degree. C. While these and other properties make these polymers useful as heat decomposable, mold patterns in the manufacture of articles by the casting of metals, and as sacrificial binders in the manufacture of articles by sintering molded ceramic and metallic powders, they also have limited the utility of these PACs.
The U.S. Pat. No. 3,706,713, to Hull et al. discloses compositions comprising polymers of carbon dioxide and one or more of aliphatic (including cycloaliphatic) 1,2-monoepoxides having at least four carbon atoms per molecule. The compositions are stated to be useful in moldings, films and fibers. The patent discloses that the polymers had crystallinity when made from cycloaliphatic epoxides, and very little crystallinity when made from isobutylene oxide.
It is well known that most polymers described as crystalline are not completely crystalline. They contain amorphous fractions. However, the crystalline fractions usually are predominate as far as polymer properties are concerned. Hence, such polymers are referred to herein as predominantly crystalline polymers.
It also is known that some predominantly crystalline polymers at temperatures in a range (depending on the polymer) below their melting points, but above normal room temperatures, can be stretched up to a point of breakage or failure, and, while maintaining them in the stretched condition, cooled to a temperature at which they will retain their stretched condition until heated to temperatures in that range or at or above their melting points. The resulting polymers, characterized by increased clarity and other physical properties including impact strength, are described as oriented. If the stretching is only in one direction as, for example, in the plane of a film of such a polymer, the polymer or film is said to be uniaxially oriented. If the stretching is in transverse directions, the polymer is described as biaxially oriented. An example of a predominantly crystalline polymer that can be oriented is predominantly crystalline polypropylene which generally has an orientation temperature range of about 140.degree.-165.degree. C. Indeed, biaxially oriented polypropylene packaging film is a well known article of commerce.
The U.S. Pat. No. 4,142,021, to Dixon et al. discloses laminates with water and oxygen barrier properties, which comprise a base layer and an adhesive barrier layer. The base layer can be polymeric, metallic or fibrous. Examples of the base layer include polyethylene, polypropylene and ethylene-propylene copolymers. The adhesive barrier layer is a PAC. The patent discloses forming the laminates by (a) solvent casting the PAC over the base layer, and evaporating the solvent, (b) applying a melt of the